On-chip optical pulse shaping using cascaded co-directional couplers
Bibliographic record
Abstract
Summary form only given. Picosecond-resolution optical pulse shaping (OPS) is desired for many important applications in ultrahigh-bit-rate optical fiber communications and ultrafast optical signal processing. Commercially available optical pulse shapers operate based on the well-established spatial-domain processing approach, allowing programmable synthesis of arbitrary waveforms with resolutions better than 100 fs. However, the need for high-quality bulk-optics components makes the implementation of this method relatively complex. Similar OPS principles have been implemented using compact on-chip arrayed diffraction gratings (ADGs), but ADGs are challenging to fabricate, yet they suffer from limited spectral resolution. All-fiber and integrated-waveguide grating structures have been considered as another solution for OPS due to their mature fabrication process and low loss (particularly in fiber-based schemes). However, grating devices have proven challenging to fabricate in integrated-waveguide configurations and it would be also difficult to add reconfigurability in these structures. To overcome the aforementioned limitations, we will review here recent work on a novel design based on a structure of cascaded co-directional couplers. In particular, our new design exploits the fact that under relatively weak-coupling conditions, the `discrete' amplitude and phase `apodization' profile of the structure can be directly mapped into the output temporal response of the device, see scheme in Fig. 1. We refer to this approach as discrete space-to-time mapping (D-STM). The proposed design is based on forward coupling between a main-waveguide and a bus-waveguide, where the coupling is controlled in a discrete fashion through standard co-directional couplers (`amplitude apodization'). On the other hand, phase tuning can be done by adjusting the relative path-length different between sections of bus and main-waveguide at each stage of the device. The devices obtained through this new design method are notably simpler to fabricate than their Bragg grating-based counterparts, while potentially enabling reconfigurability through well-established mechanisms. Using D-STM, we have successfully re-shaped (sub-)picosecond Gaussian-like pulses into several practically relevant pulse shapes, including a 1.25 ps (FWHM) long flat-top pulse, an 8-bit, 200 G-baud 16-quadrature amplitude modulation (QAM) bit sequence and a 70 ps (FW) long high quality flat-top pulse. The power spectral responses (PSRs) presented in Fig. 2, have been measured using an optical vector analyzer (O-VA). Besides, direct time-domain characterization of the output synthesized waveforms has been carried out using Fourier-transform spectral interferometry (FTSI). As shown in Fig. 2(f) a combination of single-mode waveguide (SMW) and multi-mode waveguide (MMW) has been used to reduce the loss and phase-noise for the case of long-duration OPS devices.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".